In order to perform a suitable image forming operation, an art for a conventional image forming apparatus to supply current to a conveying belt with a cleaning roller and detect the resistance of the conveying belt is known. Furthermore, because the conveying belt can be damaged or deteriorated if a voltage applying unit supplies too much current to the conveying belt, an art to detect the current (the resistance) flowing through the conveying belt and control the current is also known.
However, with an image forming apparatus using the art, the conveying belt has a portion charged by a transfer bias applied thereto, and detection of the current can be performed at the charged portion. Then, a current generated by the charge can be contained in the detected current, and the accuracy in detection of the current can be lower.
Therefore, there is a need for an image forming apparatus that has higher accuracy in detection of the current flowing through a carrier such as the conveying belt.